Enabling In-Ear Magnetic Sensing: Automatic and User Transparent Magnetometer Calibration

Earables (in-ear wearables) are a new frontier in wearables. Acting both as leisure devices, providing personal audio, as well as sensing platforms, earables could collect sensor data for the upper part of the body, subject to fewer vibrations and random movement variations than the lower parts of the body, due to inherent damping in the musculoskeletal system. These data may enable application domains such as augmented/virtual reality, medical rehabilitation, and health condition screening. Unfortunately, earables have inherent size, shape, and weight constraints limiting the type and position of the sensors on such platforms. For instance, lacking a magnetometer in all earables reference platforms, earables lack reference points. Thus, it becomes harder to work with absolute orientations. Embedding magnetometers in earables is challenging, as these rely heavily on radio (mostly Bluetooth) communication (RF) and contain magnets for magnetic-driven speakers and docking. We explore the feasibility of adding a built-in magnetometer in an earbud, presenting the first comprehensive study of the magnetic interference impacting the magnetometer when placed in an earable: both that caused by the speaker and by RF (music streaming and voice calls) are considered. We find that appropriate calibration of the magnetometer removes the offsets induced by the magnets, the speaker, and the variable interference due to BT. Further, we present an automatic, user-transparent adaptive calibration that obviates the need for alternative, expensive, and error-prone manual, or robotics, calibration procedures. Our evaluation shows how our calibration approach performs under different conditions, achieving convincing results with errors below 3° for the majority of the experiments.

I. INTRODUCTION

Recent years have seen the rise of wearable technologies, both in the form of specialist devices such as pacemakers and in consumer devices, primarily smartwatches. A growing trend is the use of wireless earbuds that, while designed primarily for personal audio playback, offer a new sensing platform at an important site on the body. So-called Earables can be equipped with a variety of sensors and radios making them potentially suitable for a range of applications that go beyond just audio streaming, including indoor navigation, augmented reality, enhanced perception and medical monitoring. Some analysts believe Earables could be as disruptive as smartphones were in the last decade – forecast to hold the largest share (35%) of the wearable market [4]. Today, however, we are in the early stages of understanding their capabilities, both in terms of the sensors that they can offer and their applications.